Rounding numbers in PHP

[SneakyDave]

Sneaky's dumb question of the day.

I can use the round() function to round a number up to an integer, but what if I want to take a percentage of "sales", say 5% of $123.78? The answer is 6.189, but using printf(), I can only achieve 6.18, not the true amount of 6.19, rounded.

Is there a simple way I can round to the nearest cent?

Thanks
Sneaky

[Justin]

Add half of your least significant digit and then do an intval() or sprintf():

7.557 rounded to the nearest cent would be 7.56 - so doing this would round to the nearest cent:

$num = 7.557;
$rounded = intval($num * 100 + .005) / 100;

Resulting in 7.56. Or to simply round to whole numbers, add .5:

$num = 8.77242985186345973654
$rounded = intval($num + .5);

Which would result in 9.

HTH

------------------
Justin Nelson
FutureQuest Support
[This message has been edited by Justin (edited 06-16-99)]

[SneakyDave]

Removed due to dumbness
[This message has been edited by SneakyDave (edited 06-16-99)]

[SneakyDave]

RAHAHGHGHGHGH!

OK, I don't know what I'm doing wrong here...
Here's the code I'm using, I want to find 5% of the variable $out_fee, which is 17.77.

Code Sample:

//Get the percentage of the number, results in 0.8885 $out_fee = $out_fee * .05; //Sprintf it down to 3 decimals, results in 0.889 $out_fee = sprintf("%01.3f",$out_fee); //Try to round it up to 0.89 $rounded = intval($out_fee * 100 + .005) / 100;

The result I get in $rounded is .88, not .89, did I completely screw it up?
Thanks
Sneaky

[This message has been edited by SneakyDave (edited 06-16-99)]

[stan]

Shouldn't that last line read


Code Sample:

$rounded = intval(($out_fee + .005) * 100) / 100;

- Stan

[Justin]

Nope - order of operations   The muliplication is always done first. There is an error however   Since we are multiplying by 100, we need to add .5, not .005

So:

$rounded = intval($out_fee * 100 + .5) / 100;

is what you are looking for. BTW - no need to reduce it to 3 decimal places first - in fact, you shouldn't. First off, cutting 0.8885 to 3 places results in 0.888 - not 0.889

So you can omit that part of it - the result is an unnecessary string conversion that converts right back into a number on the next line - it never needs to become a string value in the process. PHP does convert strings to numbers and vice-versa on the fly so you usually don't see the extra overhead involved - the work is hidden. But it is there - which is why I use intval() instead of sprintf() to reduce the digits. Working with numbers is far less work for a computer than is working with strings.

HTH

------------------
Justin Nelson
FutureQuest Support

[Justin]

Stan - I see what you meant after looking again - you are right, that would also have fixed my little bug by adding .005 before the multiplication, which yeilds the same result as adding .5 after multiplying (.005 * 100 = .5). Sorry

Either way will work now

------------------
Justin Nelson
FutureQuest Support

[SneakyDave]

Hey guys, thanks for clearning that up, I've still got a little hair left, thanks to you.

Sneaky

[SneakyDave]

But I still don't understand why this isn't working:
Look at this code:

Code Sample:

$out_fee = 1.275; print "not rounded - $out_fee "; $rounded = intval(($out_fee + .005) * 100) / 100; print "rounded - $rounded ";

The output comes out:
not rounded - 1.275
rounded - 1.27

Shouldn't it be 1.28?

And on a related note, what if I don't know if the number is going to be 3 digits behind the decimal? To use intval, wouldn't I have to shorten it to the thousandths place to make the intval work right?

Thanks both for your time, again.
Sneaky

[Terra]

Pseudo Algorithm: (just thinking out loud, I'm NO mathematician)

Rounding arbitrary length decimal numbers

value: 1.2467
count :value: decimal places(DP) == 4
subtract 1 from DP == 3
raise 10 ^ 3 == 1000
multiply :value: by 1000 == 1246.7
apply PHP round function to :value: == 1247
divide :result: by 1000 == 1.247

--next example--
value: 1.275
DP == 3
10 ^ (DP - 1) == 100
1.275 == 127.5
round(127.5) == 128
128 / 100 == 1.28

--
Terra
--No muss, No fuss--
FutureQuest

PS: Feel free to rip this to shreds...